1. Field of the Invention
The present invention relates to a wear indicator for a disc brake. The invention relates to a visible wear indicator that indicates that the friction pads have worn to such an extent that they should be replaced.
2. Related Art
FIG. 10 depicts the prior art for a conventional disc brake. The disc 3 brake has a rotor 101 rotating in association with vehicle wheels and friction pads 102.sub.1, 102.sub.2. The friction pads 102.sub.1 and 102.sub.2 are urged against the rotor 101 to brake the rotor 101. The frictional force of a lining 102a.sub.1, 102a.sub.2 of the friction pads 102.sub.1, 102.sub.2 towards the rotor 101, brakes the vehicle through the rotor 101.
More specifically, both the friction pads 102.sub.1 and 102.sub.2 are guided by a support member 103 secured to the vehicle body The friction pads 101.sub.1 and 102.sub.2 disposed between a protrusion 104a of a caliper 104 and a piston 104b which is applied with a hydraulic pressure generated in a cylinder formed on the caliper 104. When a backing plate 102b.sub.1 of one of the friction pad 102.sub.1 is urged by the piston 104b, the other backing plate 102b.sub.2 of the friction pad 102.sub.2 is also urged against the rotor 101 by the protrusion 104a of the caliper 104, so that the braking operation is performed.
The slidable backing plates 102b of the friction pads 102 are supported rotor by the support member 103 in such a manner that a groove formed on the backing plates 102b is engaged with a protruding guide portion 103a formed on the support member 103.
In the prior art, the guide portion 103a of the support member 103 is prevented from being worn out by a clip member which is fitted on the guide portion 103a of the support member 103 and disposed between the guide portion 103a and the backing plate 102b. There are several known and types of the structures of the groove and guide member depending upon design of the disc brake.
The linings 102a of the friction pad 102 are worn out due to repeated braking operations. Before the lining 102a of the friction pad 102 has worn away completely, the pad is replaced by a new one since the contact of the backing plate directly to the rotor may cause serious problems.
There has been several types of conventional wear indicator apparatus for automatically alarming the condition of non-allowable wear amount of the lining. For example, U.S. Pat. No. 4,037,689 discloses one example of the conventional apparatus in which an end of an elastic piece is fixed to a backing plate of a pad while the other end of the elastic piece extends toward the rotor. The extending end of the elastic piece comes into contact to the rotating rotor when the lining is worn out to such an extent that the pad should be replaced. This contact vibrates the apparatus which in turn generate a noise alarm.
In the other conventional apparatus, a window is formed on a top portion of the caliper permitting visual observation of the lining through the window.
FIG. 11 is a perspective view showing a second type of conventional wear indicator. In this indicator, a step down portion 113a is formed on a sliding surface of a pad of the support member 113. When the lining is worn out to and should be replaced, such a condition becomes apparent from a positional relation between the step down portion 113a and the backing plate.
However, in the conventional wear indicator apparatus having the elastic piece fitted on the backing plate of the friction pad, the number of parts increase making the assembly process complicated. Further, the alarm sound would not have a sufficient high volume, which may cause problems.
Further, the second conventional apparatus having the window, it is difficult to visually observe the pad thickness the window cannot be made sufficiently large because the structural integrity of the caliper would be seriously compromised. Thus the inside of the caliper is dark making it hard to observe the pads clearly.
Furthermore, in the other wear indicator structure as shown in FIG. 11, it is necessary to form the step down portion on the support member 113 which causes assembling process to be complicated.